Support macOS menu section headers

[artob]

macOS 14+ now supports section headers in menus:

These are menu items created with the sectionHeaderWithTitle: selector:

[menuToAddTo addItem: [NSMenuItem sectionHeaderWithTitle: text]];

References

• https://developer.apple.com/documentation/appkit/nsmenuitem/sectionheaderwithtitle:
• https://forum.juce.com/t/macos-menu-bar-section-headers/60547